1. Field of Art
The present invention relates generally to apparatus and methods for cementing downhole tubulars into a well bore. More particularly, the present invention relates to a cementing manifold and method of use.
2. Description of Related Art
A well-known method of drilling hydrocarbon wells involves disposing a drill bit at the end of a drill string and rotating the drill string from the surface utilizing either a top drive unit or a rotary table set in the drilling rig floor. As the well is formed, it is desirable to line the well bore. Thus, as drilling continues, progressively smaller diameter tubulars comprising casing and/or liner strings may be installed end-to-end to line the drilled borehole. As the well is drilled deeper, each string is run through and secured to the lower end of the previous string to line the borehole wall. The string is then cemented into place by flowing cement down the flowbore of the string and up the annulus formed by the string and the borehole wall.
To conduct the cementing operation, typically a cementing manifold is disposed between the top drive unit or rotary table and the drill string. Due to its position in the drilling assembly, the cementing manifold must suspend the weight of the drill pipe, contain pressure, transmit torque, and allow unimpeded rotation of the drill string. When utilizing a top drive unit, a separate inlet is typically provided to connect the cement lines to the cementing manifold. This allows cement to be discharged through the cementing manifold into the drill string without flowing through the top drive unit.
In operation, the cementing manifold allows fluids, such as drilling mud or cement, to flow therethrough while simultaneously enclosing and protecting from that flow, a series of projectiles, e.g., darts and spheres, that are released on demand and in sequence to perform various operations downhole. Thus, as fluid flows through the cementing manifold, the darts and/or spheres are isolated from the fluid flow until they are ready for release.
Conventional cementing manifolds are available in a variety of configurations, with the most common configuration including a single sphere/single dart manifold. Using such a device, the sphere is dropped at a predetermined time during drilling to perform a particular function. For example, a sphere may be dropped to form a temporary seal or closure of the flowbore of the drill string or to actuate a downhole tool, such as a liner hanger, in advance of the cementing operation. Once the cement has been pumped downhole, the dart is dropped to perform another operation, such as wiping cement from the inner wall of a string of downhole tubular members.
Another common cementing manifold employs a single sphere/double dart configuration. The sphere may be released to actuate a downhole tool, for example, followed by the first dart being launched immediately ahead of the cement, and the second dart being launched immediately following the cement. Thus, the dual darts cap the “ends” of the cement and prevent the cement from mixing with drilling fluid as the cement is pumped downhole through the drill string. Each dart typically also performs another operation upon reaching the bottom of the drill string, such as latching into a larger dart to wipe cement from the string of downhole tubular members.
Whether the cementing manifold includes a single sphere/single dart or single sphere/double dart configuration, there are operational characteristics common to both. Loading and certification of the cementing manifold is not performed at the drill site. Instead, the sphere and dart(s) are typically loaded into the cementing manifold, with the customer present to verify the loading procedure, prior to transporting the cementing manifold to the drill site. Also, the majority of cementing jobs require a single sphere and at most two darts. Thus, a cementing manifold with a single sphere/single dart or single sphere/double dart configuration is sufficient for most cementing jobs.
Usually, two loaded cementing manifolds, including one for backup purposes, are then transported to the drilling rig. Prior to conducting a cementing job, rotation of the drill string is interrupted so that a loaded cementing manifold may be installed between the cementing swivel and drill string. In some configurations, the cementing manifold weighs several thousand pounds and may be 13 feet in length. Thus, given the weight and size of the cementing manifold, lifting it into position, which may be 20-30 feet above the rig floor, raises concerns for the safety of rig personnel. Therefore, it is desirable to reduce the size and weight of the cementing manifold so that installation of the cementing manifold may be both safer and easier.
Once the cementing manifold is installed, rotation of the drill string may resume, at least until the cementing operation begins. As previously stated, a sphere and dart(s) are released to perform various tasks at different stages of a cementing operation. During most cementing operations, actuation of valves to release the sphere and darts is performed manually by rig personnel. Rotation of the drilling string is again interrupted to allow rig personnel to traverse the thirty or so feet above the rig floor to the cementing manifold and manually actuate valves on the cementing manifold to release the sphere and darts. This too raises safety concerns. For this reason, some cementing manifolds may now be actuated to release the sphere and darts via remote control from the rig floor. Remote control actuation also allows rotation of the drill string to continue uninterrupted because rig personnel remain on the rig floor, a safe distance from the rotating equipment.
Verification that the sphere or dart has been released from the cementing manifold is performed by visual inspection. In the case of manual actuation, as the sphere or dart exits the cementing manifold, a flag on the cementing manifold is triggered. While this flag is designed to be visible from the rig floor, resetting the flag requires rig personnel to ascend the rig to manually reset the flag, there again raising safety concerns. In the case of remote control actuation, instead of a triggered flag, rig personnel view an indicating device that changes orientation on the cementing manifold when a sphere or dart has been released. However, the indicator is often shrouded within a plate assembly, requiring the rotating speed of the drill string be reduced so that rig personnel can clearly see the indicator orientation from the rig floor.
Thus, at the minimum, releasing a sphere or dart and verifying that release requires slowing the rotation of the drill string. Further, such release and verification frequently requires rig personnel to ascend the rig to the cementing manifold, raising concerns for the safety of rig personnel. Therefore, it is desirable to remotely actuate and remotely verify the release of spheres and darts from the cementing manifold, including resetting any involved devices prior to subsequent releases, without either the need to reduce the rotation speed of the drill string or for rig personnel to position themselves in proximity of the cementing manifold.
Once the cementing operation is complete, the cementing manifold may be empty. Typically, the cementing manifold is not reloaded and recertified on the drilling rig. Rather the empty manifold is removed from the drill string and stored on the drilling rig until it can be transported back to the laboratory for reloading and recertification. Given its size, storing the cementing manifold on the drilling rig may be less than convenient. At a length of 13 feet, the cementing manifold may not fit in standard racks, requiring it to be stored elsewhere on the drilling rig and thereby consuming valuable rig space. Therefore, it is also desirable to reduce the size of the cementing manifold such that it may be easily stored in standard sized racks.